Radiolabelled monoclonal antibodies are meant to carry radioactivity to be deposited in tumor cells. The pharmaceutical and physiologic processes ultimately governing the actual distribution of antibodies, and thereby the associated dosimetry are complex. Quantitative imaging, both spatial and temporal, of radioactive nuclides is a key element as a basis of clinical dosimetry. Our group is engaged in efforts to examine the potential of combining gammacamera and CT or MRI images as a basis of clinical dosimetry. Gammacamera images are 2-dimensional (2-D) condensations of information, with relatively low resolution, while sets of CT or MRI slices provide in principle high resolution 3-D information on the underlying anatomy. Our efforts involve: A) the development of computer linkage between the two, so that areas of interest on a gammacamera scan can be located over the 3-D anatomy; B) establishing the potential for determining the distribution of radioactivity in the layers underlying an area of interest.